Cordocentesis

Cordocentesis, also called percutaneous umbilical blood sampling, takes a sample of foetal blood from the umbilical vein at or near the placental cord insertion under ultrasound imaging. It is used when foetal blood is needed for diagnosis or treatment.

The sample gives foetal haemoglobin, blood count, blood group, infection markers, karyotype and acid base status. It also allows intrauterine transfusion when a fetus is anaemic.

Usage. It is a specialist procedure, used when less invasive tests cannot answer the clinical question. The risk is higher than amniocentesis, so it is reserved for specific indications.

Indications. Rapid karyotype when amniocentesis is unhelpful or delayed, foetal anaemia assessment in alloimmunisation, foetal thrombocytopenia, suspected foetal infection (for example, parvovirus B19 IgM, cytomegalovirus or toxoplasmosis), foetal acid base assessment, and intrauterine transfusion or drug therapy.

Preparation and technique. The placental insertion of the cord is mapped by ultrasound, and the needle is placed in an umbilical vein, away from the artery. The procedure is performed in a unit with foetal monitoring and transfusion capability. Foetal heart rate is monitored throughout.

Contraindications and precautions. Active maternal infection, maternal bleeding, placental position limiting access, and foetal demise. Rh negative women are offered anti-D immunoglobulin after the procedure where indicated.

Interpretation.

• Foetal haemoglobin, blood count and reticulocyte values are compared with gestational age ranges, which differ substantially from adult values.
• Foetal blood group and antibody status are assessed in alloimmunised pregnancies.
• Infection PCR and IgM results are interpreted in the context of maternal serology and timing.
• Foetal blood gas and lactate reflect acid base status at the time of sampling.

Causes of an uninterpretable result. Maternal blood contamination, which can be identified by foetal specific haemoglobin or genetic markers, and haemolysis of the sample.

Critical values and findings needing immediate action.

• Foetal anaemia that is severe for gestational age requires urgent intrauterine transfusion planning.
• Foetal bradycardia during sampling requires immediate cessation and foetal review.

Limitations and artefacts. Maternal blood contamination lowers the foetal values and causes misinterpretation. Haemolysis affects measured values. Foetal values change over short periods, so repeat sampling may be needed.

Follow up tests. Repeat foetal blood sampling to track anaemia, serial foetal ultrasound and Doppler of the middle cerebral artery, and infection follow up with maternal and foetal serology.

Complications. Foetal bradycardia, cord haematoma, bleeding from the puncture site, miscarriage, preterm labour and infection. The risk of pregnancy loss is higher than with amniocentesis and varies with indication and experience.

Special groups. Pregnancy specific reference ranges apply throughout. Multiple pregnancy requires assessment of each fetus. Infants born after the procedure require neonatal review of the indication.